1. Field of the Invention
The present invention relates to a camera system for picking up the image of an object and a photometric and an automatic focusing method.
2. Description of the Related Art
Hitherto, in a camera capable of forming image data representative of an image of an object, there are known various photometric schemes, such as the averaged overall light sensing scheme in which the brightness of an object and its background is measured, the center-weighted light sensing scheme, the multiple segment exposure metering scheme, etc. Some types of cameras include a system in which the light metering is conducted through selectively switching the photometric schemes in the nature of an object. The photographic conditions, such as a shutter speed and a stop value, which determine exposure for photographing of an object, are determined on the basis of photometric information obtained through light metering according to the above-mentioned manner. The image data, which is representative of the image of the object photographed on the basis of the determined photographic conditions, is subjected to a predetermined processing, such as a compression processing, etc., and then stored in an information recording medium such as an optical disc, an IC memory card, etc. Further, the image data is output to a monitor device and/or a printer device so that an image represented by the image data is displayed and/or printed.
According to the conventional light metering scheme, however, it is impossible to change a photometric zone which has been set beforehand, and also impossible to optionally select a photometric zone. For example, according to the center-weighted light sensing scheme, a priority metering of only the center of photometric zone which has been set beforehand is merely made. Further, according to the multiple segment exposure metering scheme, a selective metering of the segmented photometric zones is merely made. Consequently, according to the conventional photometric schemes, it is impossible to perform an adequate exposure metering in compliance with the content of images, since the photometric zone is fixed. Thus, according to the conventional photometric scheme, if the contrast of the object is very high, or the reflection factor of the object is remarkably different from a reference reflection factor, it is difficult to form an adequate exposure value. Further, according to the conventional photometric scheme, since the photometric zone is fixed, the position of the camera needs to be changed for every operation so that the photometric zone coincides with a photometric portion of the object as a target. Specifically, in case of photographing upon fixing of the camera on a base such as a tripod, this involves such a problem that the operation for the photometry is very complicated.
Next, with respect to the automatic focusing in the camera as mentioned above, hitherto, there are known various detection schemes, such as the contrast detection scheme in which the focusing state of an object image formed by a shooting lens system is detected, and the phase difference detection scheme, etc. The automatic focusing is concerned with a system in which any of the above-mentioned detection schemes is used to detect the focal point of the shooting lens system, and the shooting lens system is moved to a detected focal point so as to obtain an image which is in focus.
For example, in a camera adopting the contrast detection scheme in which contrast information about the object is detected from an image signal which is representative of an image formed through an image shooting, a detection zone (focusing frame or AF frame) in which the contrast information of the image of the object is detected is disposed at the center of the picture field, for example. Thus, in order to attain a focusing state of the image of the object, the position of the camera is changed by an operator in such a manner that a target portion of the object image to be focused is within the focusing frame, so that the contrast information for focusing may be detected on the basis of the pickup signal involved in the focusing frame. The shooting lens system is driven in such a manner that the maximum contrast information is derived. In this case, the focusing is locked to maintain the focusing state of the image of the object, and then the position of the camera is adjusted for framing so that a desired composition of photograph is performed. As described above, according to the conventional automatic focusing system, it is possible to implement the focusing of the image of the object, through the use of the system together with the focusing lock function.
According to the conventional automatic focusing system, however, the focusing frame for determining the focusing state is fixed, and, thus the position of the camera needs to be changed for every operation and practice the focusing lock, so that the focusing frame coincides with a target portion of the object. Hence, specifically, in case of photographing upon fixing of the camera on a base such as a tripod, and a copy stand for copying documents, the fixing of the camera needs to be restarted for every operation. Thus, the operation for focusing according to the image of the object is very complicated.
Further, for example, in the contrast detection scheme, if a plurality of focusing frames are provided for the purpose of detecting a plurality of contrast information messages, all of the plurality of contrast information messages detected by the plurality of focusing frames are not necessarily needed, and thus it is difficult to determine an optimum position of the shooting lens system. In addition, in this case, it is impossible to implement the automatic focusing in such a manner that all of the objects corresponding to the plurality of focusing frames are in focus.
The demand for higher image quality of photographed images has been increased. A high image quality of image, which is photographed by a camera adapted for photographing in high image quality, is available for printing and medical uses. Under the situation, an improvement of accuracy in focusing is desired. Nevertheless, hitherto, there has been no technology proposed that selects target portion of an object in a simple way and focuses the selected portion with great accuracy.